As for a head lamp of an automobile, as one of techniques to obtain light distribution for enhancing illumination effect in a front area of an own vehicle and preventing dazzling a vehicle existing in the front area of the own vehicle such as a preceding vehicle or an oncoming vehicle existing in the front area (hereinafter, referred to as a “front vehicle”), an ADB light distribution control has been proposed. The ADB light distribution control is performed in such a manner that a front vehicle is detected by a vehicle position detection device, a light amount in an area where the detected vehicle exists is reduced or the light is turned off, and the other wide areas are illuminated brightly.
In recent years, the ADB light distribution control is also applied to a head lamp which has a light-emitting element, for example, an LED as a light source, and combines light from a plurality of LEDs as light sources, that is, respective illumination areas of respective LEDs to form light distribution for illuminating the front area of the own vehicle. Then, when a front vehicle is detected, the LED in the illumination area corresponding to the detected front vehicle is dimmed or turned off.
In this ADB light distribution control, white light emitted from a plurality of LEDs is projected through a projection lens in the front area of the own vehicle to form a plurality of illumination areas. Then, a required illumination area is formed by appropriately combining and mixing the illumination areas. However, due to the spherical aberration, for example, the chromatic aberration caused by the projection lens, dispersion of light may occur at the peripheral portion of each illumination area, and the visibility of the illumination may be deteriorated.
In order to overcome the spherical aberration, particularly the chromatic aberration of the projection lens, Japanese Patent Application No. 2015-222687 proposes a projection lens in which adopts a doublet lens including a convex lens and a concave lens, and has a gap between the convex lens and the concave lens. Further, there is proposed a projection lens in which each surface of the convex lens and the concave lens is formed as an aspherical surface.